Method for making lithium-containing magnesium alloy

ABSTRACT

A method for making lithium-containing magnesium alloy is provided. The method includes carrying out a diffusive electrolysis in an electrolyte, essentially including lithium chloride and potassium chloride, by using a graphite material as an anode and a material of a magnesium or magnesium alloy as a cathode. Therefore, the lithium is diffused into the cathode to form a raw material, lithium-magnesium master alloy, with higher weight percentage of lithium. Further, the lithium-magnesium master alloy is smelted and cast into a lithium-containing magnesium alloy with a desired lithium content.

BACKGROUND

1. Field of Invention

The present invention relates to a method for making lithium-containing magnesium alloy. More particularly, the present invention relates to a method for making lithium-containing magnesium alloy in an atmospheric environment.

2. Description of Related Art

Magnesium alloy is a lightweight, anti-seismic material that provides great specific tensile strength, heat conductivity, and an electromagnetic wave screen effect that satisfies the needs of the 3C products. Hence, the magnesium alloy is a potential material in 3C product manufacturing and design.

Because magnesium alloy provides a higher specific tensile strength than other structure alloys, it is feasible for some components of vehicle to lower the energy consuming. In addition, the recycling and reuse properties also make magnesium alloy becomes the most popular material structure.

The lithium-magnesium alloy has excellent specific tensile strength, coefficient of elasticity, and is light. However, magnesium has poor malleability and plasticity because magnesium crystals have a hexagonal close packed structure (HCP). The solution to the problem is to heat the magnesium, however, magnesium oxidation is extremely active when magnesium is heated in air and exothermic reactions and ignition may occur.

Conventionally, lithium-magnesium alloy is prepared by putting solid lithium into a magnesium melt to smelt and cast the lithium-containing magnesium alloy. However, solid lithium is extremely unstable in air because of the humidity among the air may result in dangerous flash lithium gasification. High-frequency induction furnace is needed for melting the lithium in vacuum condition and surrounds the lithium with a protective gas, argon. Therefore, the conventional process of preparing a lithium-containing alloy is not only difficult to operate but also expensive, and consequently limits the application of lithium-containing magnesium alloys.

Solid lithium is very dangerous during the hauling and storage period, so the price difference of solid lithium depends on the transportability, and the cost cannot be lowered in regions without lithium ore that relies on importing the lithium from the place of origin.

SUMMARY

The method for making lithium-containing magnesium alloy in accordance with the embodiment of the invention comprises several steps. The first step is diffusing a lithium material into a magnesium (or magnesium alloy) cathode material by a diffusive electrolysis process. The diffusive electrolysis may proceed in an atmospheric environment to form a lithium-magnesium master alloy within the range of Mg-10 wt. % Li˜Mg-50 wt. % Li, the lithium concentration of the master alloy is within the range of 10˜50% by weight. Then, the lithium-magnesium master alloy is used as a raw material to further smelt and cast the lithium-containing magnesium with the desired lithium content.

As embodied and broadly described herein, the method provides a more safe and economical way to produce lithium-containing magnesium alloy.

In this embodiment, diffusive electrolysis initially diffuses lithium into a magnesium (or magnesium alloy) material in an atmospheric environment to form a lithium-magnesium master alloy. The master alloy can be hauled and stored in an atmospheric environment, solved the problem of highly activity of solid lithium in atmospheric environment.

In addition, the lithium concentration of the master alloy may be quantified in an advance with composition analysis, and the final lithium content of the product, lithium-containing magnesium alloy, is controllable.

It is to be understood that both the foregoing general description and the following detailed description are by examples, and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the embodiment of present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:

FIG. 1 is a flowchart of steps in accordance with an embodiment of the present invention; and

FIG. 2 is an operational cross-section view of a specific electrolytic bath when the diffusive electrolysis is in progress therein.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.

Refer to FIG. 1. FIG. 1 is a flowchart of steps in accordance with an embodiment of the present invention. First, as shown in step 110, an electrolytic bath processes diffusive electrolysis of lithium in air.

Refer to FIG. 2. FIG. 2 shows a cross-section view of the electrolytic bath when the diffusive electrolysis is in progress therein. The electrolytic bath 200 possess a double-decked structure, which comprises an external bath 210, an alumina inner bath 220, and a movable lid 211 covered on the top of external bath 210.

A plank 221 is set in the bottom of the alumina inner bath 220, and a steel container 230 is mounted on the plank 221. A glass container 240 is settled in the steel container 230 to load an electrolyte 241. In accordance with an embodiment of the invention, the electrolyte 241 essentially consists of 45% by weight (wt. %) of lithium chloride and 55% by weight of potassium chloride.

A heater 250 is placed between the alumina inner bath 220 and steel container 230 to heat the electrolyte 241, and a thermocouple 260 dipped into the electrolyte 241 monitors the variation of temperature in the electrolytic system.

An anode 242 and a cathode 243 are set up on the glass container 240 and dipped into the electrolyte 241. The anode 242 and cathode 243 are joined together by a cathode supporter 244, and the lower tip of the cathode supporter 244 provides an alumina-tubing 245. A gas 246 is puffed through the alumina-tubing 245 to the electrolyte 241.

In accordance with an embodiment of the present invention, a graphite material is used as the anode 242, and a magnesium or magnesium alloy is used as the cathode. Moreover, in consideration of the preferred superficial of the auxiliary electrode (UE, anode 242) must 100 fold greater than the working electrode (WE, cathode 243), the surface of the anode 242 is drilled to increase the superficial to perform the electrolysis. Therefore, the polarization exerted from exterior has more affect on the cathode 243.

Then, as shown in step 120, performing a diffusive electrolysis to diffuse the lithium material into the cathode 243, and form a lithium-magnesium master alloy. The master alloy contains lithium with a concentration within the range of 10˜50% by weight (wt. %). The reaction occurred in the electrolyte system is shown as follow:

LiCl→Li⁺+→Cl⁻

KCl→K⁺+Cl⁻

Then, the reduction reaction on the cathode 243 is:

Li⁺+e⁻→Li

K⁺+e⁻→K

In accordance with an embodiment of the present invention, the working temperature of the diffusive electrolysis is controlled within a range of 400˜530° C. to provide the electrolysis system with a high temperature. Then, a 3V˜4.2V direct current is exerted on the electrolysis system to form a lithium-magnesium master alloy. As the result of the treatments, the nature of the lithium-magnesium master alloy is more stable than solid lithium, and the alloy provides high lithium content within the range of 10˜50% by weight (wt. %) for further making a lithium-containing magnesium alloy.

In contrast with solid lithium material, the lithium-magnesium master alloy is an inactive material applicable to smelt and cast in an atmospheric environment. Therefore, the manufacturing of lithium-containing magnesium alloy is more safe, and the final lithium content of the lithium-containing magnesium alloy is controllable.

Finally, as shown in step 130, the master alloy is smelted by general manner to cast a lithium-containing magnesium with the desired lithium content, such as the commercial lithium-magnesium alloy, Mg-9 wt. % Li-1 wt. % Zn, or any lithium percentage of alloys.

In according to above-mentioned, the method of produce lithium-containing magnesium alloy has several advantages:

First, the embodiments show the raw material, lithium-magnesium master alloy, is prepared by a diffusive electrolysis in an atmospheric environment that exceeds the safety of the conventional process. The operations of diffusive electrolysis obviate the danger of solid lithium ignition in air, and therefore save the cost for vacuum equipment.

In addition, the raw material, lithium-magnesium master alloy, is a stable material in air that minimizes the danger during the transportation and storage period. Hence, employing the master alloy as the raw material of lithium-containing magnesium alloy lowers the transportation cost.

Moreover, the lithium content of the lithium-containing magnesium alloy is controllable by using an advanced composition analysis of the master alloy that simplifies the quality control of reproduction.

It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the embodiments of present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents. 

1. A method for making lithium-containing magnesium alloy, the method comprising the steps of: diffusing a lithium material into a cathode material by diffusive electrolysis; forming a lithium-magnesium master alloy containing lithium within the range of 10˜50% by weight (wt. %); and smelting the lithium-magnesium master alloy to cast a lithium-containing magnesium with a desired lithium content.
 2. The method of claim 1, wherein the diffusive electrolysis uses a graphite material as an anode to diffuse the lithium material into the cathode in an electrolyte.
 3. The method of claim 2, wherein the electrolyte essentially consists of 45 wt. % lithium chloride and 55 wt. % potassium chloride.
 4. The method of claim 1, further comprising: performing an advanced composition analysis before smelting the lithium-magnesium master alloy to quantify the lithium concentration.
 5. The method of claim 1, wherein the lithium-magnesium master alloy is smelted and casted in atmospheric environment.
 6. The method of claim 1, wherein the working temperature of the diffusive electrolysis is kept within a range of 400˜530° C.
 7. The method of claim 1, wherein the diffusive electrolysis uses a 3V˜4.2V direct current as a working current. 